ABSTRACT
This chapter will look at the analysis of variance of two factors and their interaction. Two-way analysis of variance compares the means of groups made up of two variables or factors. The two factors in our example are sex and treatment. With two categories or levels of sex and three of treatment (no tutorial, individual tutorial and group tutorial), we have what is known as a 2 × 3 analysis of variance. If we just had two levels of treatment (e.g. no tutorial and group tutorial), we would have a 2 × 2 analysis of variance. The variable being compared is often called the dependent variable because it is usually assumed that the values of this variable depend on, or are affected by, the factors being investigated. As a consequence, the factors being investigated are frequently referred to as independent variables since in the design they are not thought to be affected by the dependent variable. Furthermore, their statistical association with the dependent variable is called an effect.
